<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8"/>
    <title>Document</title>
    <style>
        video {
            border: 1px solid #ccc;
            display: block;
            margin: 0 0 20px 0;
            float:left;
        }
        #canvas {
            margin-top: 20px;
            border: 1px solid #ccc;
            display: block;
        }
    </style>
</head>
<body>
<video id="video" width="500" height="400" autoplay="autoplay"></video>
<canvas id="canvas" width="500" height="400"></canvas>
<button id="snap">拍照</button>
<script type="text/javascript">
    var context = canvas.getContext("2d");
    //当DOM树构建完成的时候就会执行DOMContentLoaded事件
    window.addEventListener("DOMContentLoaded", function() {
        //获得Canvas对象
        var canvas = document.getElementById("canvas");
        //获得video摄像头区域
        var video = document.getElementById("video");
        var videoObj = {
            "video" : true
        };
        var errBack = function(error) {
            console.log("Video capture error: ", error.code);
        };
        //获得摄像头并显示到video区域
        if (navigator.getUserMedia) { // Standard
            navigator.getUserMedia(videoObj, function(stream) {
                video.src = stream;
                video.play();
            }, errBack);
        } else if (navigator.webkitGetUserMedia) { // WebKit-prefixed
            navigator.webkitGetUserMedia(videoObj, function(stream) {
                video.src = window.webkitURL.createObjectURL(stream);
                video.play();
            }, errBack);
        } else if (navigator.mozGetUserMedia) { // Firefox-prefixed
            navigator.mozGetUserMedia(videoObj, function(stream) {
                video.src = window.URL.createObjectURL(stream);
                video.play();
            }, errBack);
        }
    }, false);
    // 触发拍照动作
    document.getElementById("snap").addEventListener("click", function() {
        context.drawImage(video, 0, 0, 640, 480);
    });
</script>
</body>
</html>